1. Field of the Invention
This invention relates to a method and apparatus for perforating a wellbore. In one aspect, this invention relates to the use of laser energy for perforating wellbores. In one aspect, this invention relates to a method and apparatus for removal of solids generated during the wellbore perforation process. In one aspect, this invention relates to a method of providing a clear path for transmission of laser energy in a wellbore.
2. Description of Related Art
Once the drilling of a well has been completed, fluid flow into the well is initiated by perforation of the well casing or liner. Such perforations are created using shaped charges for establishing flow of oil or gas from the geologic formations into the wellbore. The perforations typically extend a few inches into the formation. However, there are numerous problems with this approach. First, the melt or debris from shaped charges usually reduces the permeability of the producing formations resulting in a substantial reduction in production rate. Second, these techniques involve the transportation and handling of high power explosives and are causes of serious safety and security concerns. Third, the energy jet into the formation also produces fine grains that can plug the pore throat, thereby reducing the production rate.
Additionally, other steps for initiating fluid flow may also be required, depending, at least in part, on the physical properties of the fluid in question and the characteristics of the rock formation surrounding the well. Fluid flow may be inhibited in situations involving highly viscous fluids and/or low permeability formations. Highly viscous fluids do not flow easily. As a result of the decreased rate of flow, efficiency is lowered and overall production rate decreases. The same is true for low permeability formations. In extreme cases, these factors reduce the flow rate to zero, halting production entirely.
Newer technologies have employed lasers to make perforations, but perforation depths have been limited to about 4 inches after which further penetration is hampered by hole taper issues and the lack of efficient debris removal. Hole taper occurs when a collimated laser beam is utilized because of the Gaussian beam shape distribution and attenuation of the laser beam with the debris column in the hole. The edges of the beam contain less irradiance than the center of the beam as a result of which, as the perforation gets deeper, the hole eventually comes to a point and the laser beam can no longer penetrate.
U.S. Pat. No. 6,880,646 to Batarseh teaches a method and apparatus for wellbore perforation using laser energy to heat a portion of the wellbore wall to a temperature sufficient to initiate a flow of fluid into the wellbore. However, there are no teachings regarding the effect of drilling fluid or other media in the wellbore on the transmission of the laser energy to the wellbore wall, nor are there any teachings regarding handling of any debris generated by the laser operation.